Filler-reinforced polymer composites (FRPC) have been widely used in automobile, household, biomedical and electrical industries due to their enhanced stiffness, hardness, and dimensional stability. However, the tensile and impact strength of these composites is weak, which is attributed to the difference in surface energy between the in-organic fillers and polymer matrix. Therefore, improving the interfacial adhesion between the in-organic fillers and the polymer matrix by modifying the filler surface is desirable.
In order to improve the compatibility between the fillers and the polymer matrix as well as to optimize the mechanical and other physical properties, many attempts have been tried to increase the applicability of FRPCs.
The traditional method to treat filler surface by low molecular coupling agents or surfactants has found to be reasonably effective. However, the low molecular weight compounds hare the tendency to migrate out from the interface to the surface of FRPC, As a consequence, although the stiffness of composite is improved, the tensile and impact strength on the other hand is degraded remarkably. Moreover, undesirable surface appearance due to surface scorching or bulging will be resulted. In order to enhance the stiffness and toughness of FRPC, an elastomer interlayer such as butadiene acrylonitrile copolymer is coated on the filler surface before being incorporated into the polymer matrix. However, the non-homogeneity of filler distribution greatly reduces the toughening effectiveness. Another method for surface modification is by plasma treatment, as described in International Journal of Adhesion and Adhesives, Vol. 21, pages 129-136 (2001) and Composites. Part A, Vol 30, pages 405-409(1999), which enables a structural change in the interface so as to increase the compatibility between the fillers and the polymer matrix. However, this method has some limitations in engineering applications.
At present, some new approaches, such as sol-gel processing, in-situ intercalative polymerization, and in-situ polymerization, have been developed for particulate surface treatment to produce high performance FRPC. For the sol-gel processing, as described in Polymer, Vol 39, pages 6243-6250 (1998), it provides a good means for the preparation of in-organic metal oxides from organic metal alkoxides, but the formation of a cross-linking network of organic metal oxides makes it difficult to process. As a result, the widespread application of this method is limited. In-situ intercalative polymerization, which has been described in J. Polym. Sci., Polym. Phys. Edt., Vol.36, pages789-795 (1998), is a good method for production of polymer/clay composites or nano-composites, such as PA6/montmorillonite hybrid. However, this method is limited to the preparation of high-performance clay filled polymer composites, which has been described in U.S. Pat. Nos. 5,883,173 and 6,232,388. Recently, another new fabrication method called xe2x80x9cin-situ polymerizationxe2x80x9d has been developed. In-situ polymerization is a process in which inorganic particles are firstly dispersed into suitable monomers and this mixture is then polymerized using the technique similar to bulk polymerization. By this technique, the high-performance composites can be directly prepared, which has been described in U.S. Pat. Nos. 4,804,427, and 5,770,303. If the technique is used to modify the surface of in-organic filler, the polymer layer coated on the particles reduces particle surface energy as well as promotes the dispersion of the in-organic fillers in the polymer matrix. However, the degree of polymer layer grafting onto the surface fillers is very low, so the effects of reinforcing and toughening of in-organic fillers on the polymer matrix are limited. It has been described in J. Appl. Polym. Sci., Vol. 80, pages 2105-2112 (2001).
It is an object of the present invention to overcome or substantially ameliorate at least one of the above disadvantages.
It is another object of the present invention to provide an in-organic filler modified by in-situ co-polymerization of first and second monomers.
It is a further object of the present invention to take a modified in-organic filler treated by the in-situ co-polymerization and use them to fill a polymer matrix.
It is a general object of the present invention to provide reinforced and toughened composites.
There is disclosed herein an in-organic filler for a polymer matrix modified by in-situ co-polymerization of the first and second monomers. Preferably the first monomer is vinyl siloxane.
Preferably the second monomer is another vinyl monomer.
Preferably the in-organic filler includes but is not limited to talc, mica, calcium carbonate, glass bead, quartz, hydroxypatite and clay.
There is further disclosed herein a method of forming a polymer matrix comprising the steps of modifying an in-organic filler by in-situ co-polymerization of first and second monomers, and filling a polymer matrix with the filler.
Preferably the first monomer is vinyl silane.
Preferably the second monomer is another vinyl monomer.
Preferably the first and second monomers are selected such that the first monomer couples with filler by Sixe2x80x94O bonds and remaining vinyl groups on the surface of the firstly treated filler then co-polymerize with the second monomer.
Preferably the polymer of the second monomer is chosen to be miscible or compatible with the polymer matrix of the composites.
Preferably the first monomer is selected from a silane with a functional vinyl group, including, but not being limited to, tri-ethyloxyl vinyl silane (TEOVS) and tri-methyloxyl vinyl silane (TMOVS).
Preferably the second monomer has functional vinyl group, including but not being limited to methyl methacrylate, butyl methacrylate, styrene and acrylamide.